In recent years, there is a demand for performance enhancement of storage apparatuses along with the advancement of technologies. Particularly, there is a demand for storage of data, which continue to increase dramatically, and for high-speed I/O (Input/Output) processing on the storage media.
Patent Literature 1 discloses a technique to hierarchize and control storage areas. According to the technique described in this Patent Literature 1, the storage areas are hierarchized and managed based on I/O performance and reliability. Then, on the basis of access frequency, data which require the I/O performance are located in a high tier; and on the other hand, data which do not require the I/O performance are located in a low tier. Moreover, data are migrated as appropriate between the tiers based on the status of the I/O processing. Accordingly, it is intended to process inputs and outputs at high speed.